RAB8 is involved in trafficking from the trans-Golgi network (TGN) to the plasma membrane, contributes, with RAB10, 13 and 14 to GLUT4 transport, and plays a role in the formation of the primary cilium (Huber et al, 1993; Ishikura et al, 2008; Sun et al, 2010; Nachury et al, 2007; Yoshimura et al, 2007; reviewed in Hoffman and Elmendorf, 2011; Reiter et al, 2012). RAB8 also plays a role in regulating G2/M transition in complex with Optineurin (OPTN) (Kachaner et al, 2012).
RAB3IP is the best characterized GEF for RAB8A, with established roles in ciliogenesis (Hatulla et al, 2002; Knodler et al, 2010; Westlake et al, 2012; Wang et al, 2012; Feng et al, 2012; reviewed in Sung and Leroux, 2013). Other potential RAB8 GEFs include RAB3IPL and DENND1C (Yoshimura et al, 2010; reviewed in Ishida et al, 2016). Interaction of RAB8 with its GEFs displaces the GDI or CHM protein that keeps the inactive RAB:GDP soluble in the cytosol and promotes membrane association of RAB8 (reviewed in Wandinger-Ness and Zerial, 2014; Ishida et al, 2016)